A major challenge of cancer treatment is the selection of therapeutic regimens that maximize efficacy and minimize toxicity for a given patient. A related challenge lies in the attempt to provide accurate diagnostic, prognostic and predictive information. At present, tumors are generally classified under the tumor-node-metastasis (TNM) system. This system, which uses the size of the tumor, the presence or absence of tumor in regional lymph nodes, and the presence or absence of distant metastases, to assign a stage to the tumor is described in the AJCC Cancer Staging Manual, Lippincott, 5th ed., pp. 171-180 (1997). The assigned stage is used as a basis for selection of appropriate therapy and for prognostic purposes. In addition to the TNM parameters, morphologic appearance is used to further classify tumors into tumor types and thereby aid in selection of appropriate therapy. However, this approach has serious limitations. Tumors with similar histopathologic appearance can exhibit significant variability in terms of clinical course and response to therapy. For example, some tumors are rapidly progressive while others are not. Some tumors respond readily to hormonal therapy or chemotherapy while others are resistant.
Assays for cell surface markers, e.g., using immunohistochemistry, have provided means for dividing certain tumor types into subclasses. For example, one factor considered in prognosis and treatment decisions for breast cancer is the presence or absence of the estrogen receptor (ER) in tumor samples. ER-positive breast cancers typically respond much more readily to hormonal therapies such as tamoxifen, which acts as an anti-estrogen in breast tissue, than ER-negative tumors. Though useful, these analyses only in part predict the clinical behavior of breast tumors. There is phenotypic diversity present in cancers that current diagnostic tools fail to detect. As a consequence, there is still much controversy over how to stratify patients amongst potential treatments in order to optimize outcome (e.g., for breast cancer see “NIH Consensus Development Conference Statement: Adjuvant Therapy for Breast Cancer, Nov. 1-3, 2000”, J. Nat. Cancer Inst. Monographs, 30:5-15, 2001 and Di Leo et al., Int. J. Clin. Oncol. 7:245-253, 2002).
For example, the over-expression of the HER2 protein in a subset of breast cancers (HER2+) is associated with higher grade tumors that are more likely to demonstrate nodal involvement and decreased survival. Despite these distinctive clinicopathologic features, significant heterogeneity exists among patients with HER2+ disease with roughly half of these tumors expressing steroid hormone receptors, as well as demonstrating varying degrees of responsiveness to Trastuzumab (Herceptin™) targeted therapy. The identification of additional factors that could help better define the clinical diversity of HER2+ tumors would benefit therapeutic decision-making and suggest new molecular targets to overcome Trastuzumab (Herceptin™) resistance.
There clearly exists a need for improved methods and reagents for classifying tumors. Once these methods and reagents are available, clinical studies can be performed that will allow the identification of classes or subclasses of patients having different prognosis and/or responses to therapy. Such prognostic tools will allow more rationally based choices governing the aggressiveness of therapeutic interventions; such predictive tools will also be useful for directing patients into appropriate treatment protocols.